32 seconds, f11 @ 25 iso (RAW file)
There are a handful of hot pixels in the deep shadows that can be taken out easily with either the Single Pixel slider in Capture One or the "Clean Long Exposures" option in Leaf Capture
Other than that I think this is a good example of what the Aptus 22 can do in certain conditions. Low ambient temperature can always help!
Regarding the dark frame; it is taken automatically (and then calculated) whenever the exposure goes beyond 1/15 or if you change the exposure time (for example if you work in P mode)
If you do consecutive long exposures and see noise building up you can change back to a short one (e.g. 1/125) to force the back to reset itself and then carry on.
The Aptus 75, being a stop faster, will give you shutter speeds twice as long for the same exposure and since the files are bigger the noise will be less visible at the same print size